SIP is an application-layer control protocol that can establish, modify and terminate multimedia sessions or calls. SIP has been gaining in popularity and is considered likely to be the protocol of preference for application layer control of multimedia and IP telephony services, and is indeed the protocol considered to be selected to be used within 3GPP for multimedia sessions over IP to the terminal.
The current developments of SIP, however, are mainly over wireline systems where the length of the SIP messages has not been an important issue.
SIP is a text-based protocol that has great flexibility and is easy to understand. However, particularly in the application to mobile networks, the SIP messages have to carry information about the SIP proxy servers which are involved in the call session, as well as, information about those SIP proxy servers that may wish to be involved in the rest of the call session also. This can result in considerable header information being carried with each SIP message.
It is considered desirable that the session control protocol should not have lengthy messages. When SIP is applied on a wireless mobile interface, which is considered to be a relatively expensive resource, the length of the SIP messages are therefore considered unacceptable and an inefficient utilisation of a very expensive resource.
Furthermore, wireless mobile interfaces are considered to have relatively high error rates and unnecessarily lengthy messages such as the prior art SIP messages rioted above are considered more susceptible to corruption by virtue of their length.
Unfortunately, the SIP messages of the prior art, which are already considered to be quite lengthy, may grow even longer as more functionality is developed for SIP.
The present invention seeks as an object to alleviate at least one problem associated with the prior art.
Statements regarding the prior art throughout this specification are not to be taken as an admission of the state of common general knowledge in Australia in the field of the invention at the priority date of this application.